<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport"
        content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.js"></script>
    <link href="https://cdn.bootcdn.net/ajax/libs/font-awesome/5.15.1/css/all.css" rel="stylesheet">
    <style>
        * {
            font-family: 'montserrat', sans-serif;
        }

        body {
            padding: 0;
            margin: 0;
            box-sizing: border-box;
            background: #333;
        }

        .login-box {
            position: absolute;
            top: 0;
            left: -100%;
            width: 100%;
            height: 100%;
            background-image: linear-gradient(45deg, #9fbaa8, #31354c);
            transition: 0.4s;
        }

        .login-form {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            color: white;
            text-align: center;
        }

        .login-form h1 {
            font-weight: 400;
            margin-top: 0;
        }

        .txtb {
            display: block;
            width: 240px;
            background-color: #ffffff28;
            border: 1px solid white;
            padding: 10px 20px;
            color: white;
            outline: none;
            margin: 10px 0;
            border-radius: 6px;
            text-align: center;
        }

        .login-btn {
            width: 240px;
            background: #2c3e50;
            border: 0;
            color: white;
            padding: 10px;
            border-radius: 6px;
            cursor: pointer;
        }

        .hide-login-btn {
            color: #000;
            position: absolute;
            top: 40px;
            right: 40px;
            cursor: pointer;
            font-size: 24px;
            opacity: .7;
        }

        .show-login-btn {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            color: white;
            border: 2px solid;
            padding: 10px;
            cursor: pointer;
        }

        .showed {
            left: 0;
        }
    </style>
</head>

<body>
    <div class="show-login-btn">
        <i class="fas fa-sign-in-alt" style="margin-right: 5px;"></i>Show Login Form
    </div>
    <div class="login-box">
        <div class="hide-login-btn"><i class="fas fa-times"></i></div>
        <form action="index.html" class="login-form" method="POST">
            <h1>Welcome</h1>
            <input class="txtb" type="text" name="" id="" placeholder="Username">
            <input class="txtb" type="password" name="" id="" placeholder="Password">
            <input class="login-btn" type="submit" name="" id="" value="Login">
        </form>
    </div>
    <script>
        $(".show-login-btn").on("click", function () {
            $('.login-box').toggleClass('showed')
        })
        // toggleClass如果有就移除没有就添加
        $(".hide-login-btn").on("click", function () {
            $('.login-box').toggleClass('showed')
        })
    </script>
</body>

</html>